Christopher S. Swezey

Response of aeolian systems to Holocene climatic and hydrologic changes on the northern margin of the Sahara: a high-resolution record from the Chott Rharsa basin, Tunisia

Four millennial-scale latest Pleistocene to Holocene climatic cycles are recorded by aeolian-lacus trine strata along the southern margin of Chott Rharsa, a playa situated within an active tectonic basin along the northern margin of the Sahara Desert in Tunisia. Cycles are characterized by (1) a humid phase of dunefield stabilization and high lake levels, and (2) an arid phase of playa desiccation and deflation with dunefield construction. The cycles overall define a progressive drying trend and correlate well with a detailed chronology from Morocco and with the Sahara region in general for the latest Pleistocene and early Holocene. Climatic events appear more regional in nature for the later Holocene. An isolated outcrop of aeolian deposits dated at >86 ka BP argues for records of older cycles in the Chott Rharsa Basin that were subsequently removed by long-term deflation in the area.

Structural controls on Quaternary depocentres within the Chotts Trough region of southern Tunisia

Abstract The Chotts Trough of southern Tunisia is a sedimentary basin that lies immediately north of the Saharan platform. Within this basin there exist several structurally controlled depocentres, which were created by Miocene to Early Pleistocene compression associated with the Atlas orogeny. One of these depocentres, the Chott Djerid basin, has an average Quaternary subsidence rate of 0.01–0.27 mm yr 1 . Additional structural features within the Chotts Trough include east-west trending anticlines and synclines, at least some of which are controlled by east-west striking subsurface faults and northwest striking right-lateral strike-slip faults. Present movement along the northwest striking faults is a direct consequence of the Africa-Europe collision. The northwest striking faults and the east-west striking faults have cut the Chotts Trough into numerous smaller structural blocks, which experience different rates of subsidence. For the Quaternary, subsidence is caused by local extension associated with movement along the various strike-slip faults.

The lifespan of the complexe terminal aquifer, Algerian-Tunisian Sahara

Abstract The Complexe Terminal Aquifer is a multi-layered aquifer that supports a thriving date industry in the Algerian-Tunisian Sahara. Although there are numerous uncertainties regarding the exact size of this aquifer and the amount of water in place, it is certain that more water is being removed from the aquifer than is replenished by recharge. Calculations of aquifer volume, discharge rates, and recharge rates indicate that the lifespan of the Complexe Terminal Aquifer is limited, and that depletion of the aquifer will probably occur sometime well before the year 2266.

Regional stratigraphy and petroleum systems of the Appalachian Basin, North America

Figure 1.—Regional stratigraphy and petroleum systems of the Appalachian Basin, North America. Stratigraphic data are modified from AAPG (1985a,b) and Sanford (1993). The time scale is taken from Harland and others (1990); informal North American chronostratigraphic terms from AAPG (1985a,b) are shown in parentheses. Sequences and sequence boundary locations are from Sloss (1963, 1988) and Wheeler (1963). Data on petroleum source rocks are compiled from Roen and Walker (1996). Names of petroleum plays are from Roen and Walker (1996); additional information on Alabama petroleum plays is from Epsman (1987). Figure 2.—Extent of the Appalachian Basin is shown in red. The basin is subdivided into 24 regions, and the generalized stratigraphy of each region is depicted in figure 1. Column numbers in figure 1 correspond to region numbers in figure 2. Figure modified from AAPG (1985a) and from Sanford (1993). 45° N

The Identification of Eolian Sands and Sandstones

This paper presents a brief review of criteria used for identifying eolian sands and sandstones. Many features of eolian sand grains are not unique to eolian environments, and therefore one must be very careful in making environmental interpretations based only upon sand grain characteristics. The identification of stratification types provides another potential means of identifying eolian sands and sandstones. In particular, ripple laminae are very different in eolian and subaqueous systems, and the proper identification of wind-ripple laminae is an excellent method of identifying eolian sands and sandstones.

Sandstone depositional environments of the Upper Permian Champenay Formation, Champenay Basin, northeastern France

Abstract The Upper Permian Champenay Formation was deposited in a series of continental basins in northeastern France. Within the lower part of this formation, there is a sandstone of controversial origin. In the Champenay Basin, this sandstone of the Champenay Formation is exposed in three quarries between the towns of Champenay and Belval. In these quarries the sandstone is composed of deposits from deltaic, lacustrine, beach, alluvial, and eolian environments. Interpretation of these deposits suggests that the Champenay Basin was occupied by a lake, and that deltaic sediments prograded into this lake from the southeast. Relative changes in lake level resulted in the development of bounding surfaces among the deltaic sediments. Debris flows, ephemeral sheet flows, beach deposits, and eolian dunes were also present along the southern margin of this lake. The eolian dunes were crescentic in shape and migrated to the northwest. Sediment entered the southern margin of the Champenay Basin and was then redistributed and reworked by deltaic, lacustrine, beach, and eolian processes.

The Geology of Burnsville Cove, Bath and Highland Counties, Virginia

Burnsville Cove is a karst region in Bath and Highland Counties of Virginia. A new geologic map of the area reveals various units of limestone, sandstone, and siliciclastic mudstone (shale) of Silurian through Devonian age, as well as structural features such as northeast-trending anticlines and synclines, minor thrust faults, and prominent joints. Quaternary features include erosional (strath) terraces and accumulations of mud, sand, and gravel. The caves of Burnsville Cove are located within predominantly carbonate strata above the Silurian Williamsport Sandstone and below the Devonian Oriskany Sandstone. Most of the caves are located within the Silurian Tonoloway Limestone, rather than the Silurian-Devonian Keyser Limestone as reported previously.